1. Field of Invention
This invention relates to apparatus for the measurement of angular velocity of rotating devices and has application in the area of digital speedometers and the like.
2. Description of Prior Art
The function of the present invention is to produce a pulse train whose instantaneous repetition rate represents the instantaneous angular velocity of a rotating device. This pulse train may be directed into appropriate electronic circuitry for digital readout of, for example, the rate of revolution of the device or the linear speed of a vehicle in which the rotating device comprises or is coupled to a portion of the drive train.
The magnetic pulser is perhaps the most closely related prior art device. Here, a steel gear-like rotor is coupled to a rotating shaft. A permanent magnet is aligned so that the tips of the "gear" teeth successively come into close proximity to the tip of the magnet while the device rotates. The permanent magnet is surrounded by a coil. The magnetic flux is at a maximum when the magnet and a tooth are in line and decreases to a minimum when they are out-of-line. This causes a voltage to be generated in the coil due to the rate of change of magnetic flux. A voltage pulse is, therefore, generated as each tooth passes the magnet, the ultimate pulse repetition rate being proportional to the angular velocity of the rotor and, therefore, of the shaft.
The induced voltage in the coil is proportional to the rate of change of magnetic flux. Therefore, at very low rotation speeds, pulses of very low amplitude are generated. However, flip-flops and similar digital electronic circuit elements must be operated above their threshold voltages. Therefore, if an ordinary magnetic pulser is coupled with a digital readout circuit, erratic results will be obtained when the angular velocity of the shaft is below a certain level.